nRF21540 DK

Overview

The nRF21540 DK (PCA10112) shows possibility of the Nordic Semiconductor nRF21540 Front End Module connected with nRF52840 ARM Cortex-M4F CPU. The CPU provides support for the following devices:

  • ADC

  • CLOCK

  • FLASH

  • GPIO

  • I2C

  • MPU

  • NVIC

  • PWM

  • RADIO (Bluetooth Low Energy and 802.15.4)

  • RTC

  • Segger RTT (RTT Console)

  • SPI

  • UART

  • USB

  • WDT

nRF21540 DK

nRF21540 DK (Credit: Nordic Semiconductor)

More information about the board can be found at the nRF21540 website 2. The Nordic Semiconductor Infocenter 1 contains the processor’s and front end module’s information and the datasheet.

Hardware

The nRF52840 on the nRF21540 DK has two external oscillators. The frequency of the slow clock is 32.768 kHz. The frequency of the main clock is 32 MHz.

Supported Features

The nrf21540dk_nrf52840 board configuration supports the following hardware features:

Interface

Controller

Driver/Component

ADC

on-chip

adc

CLOCK

on-chip

clock_control

FLASH

on-chip

flash

GPIO

on-chip

gpio

I2C(M)

on-chip

i2c

MPU

on-chip

arch/arm

NVIC

on-chip

arch/arm

PWM

on-chip

pwm

RADIO

on-chip

Bluetooth, ieee802154

RTC

on-chip

system clock

RTT

Segger

console

SPI(M/S)

on-chip

spi

UART

on-chip

serial

USB

on-chip

usb

WDT

on-chip

watchdog

Other hardware features are not supported by the Zephyr kernel. See nRF52840 Product Specification 3 and Nordic Semiconductor Infocenter 1 for a complete list of nRF21540 Development Kit board hardware features.

Connections and IOs

LED

  • LED1 (green) = P0.13

  • LED2 (green) = P0.14

  • LED3 (green) = P0.15

  • LED4 (green) = P0.16

Push buttons

  • BUTTON1 = SW1 = P0.11

  • BUTTON2 = SW2 = P0.12

  • BUTTON3 = SW3 = P0.24

  • BUTTON4 = SW4 = P0.25

  • BOOT = SW5 = boot/reset

Front End Module

  • MOSI = P1.13

  • MISO = P1.14

  • CLOCK = P1.15

  • CHIP SELECT = P0.21

  • PDN = P0.23

  • MODE = P0.17

  • RXEN = P0.19

  • ANTSEL = P0.20

  • TXEN = P0.22

Programming and Debugging

Applications for the nrf21540dk_nrf52840 board configuration can be built, flashed, and debugged in the usual way. See Building an Application and Run an Application for more details on building and running.

Flashing

Follow the instructions in the Nordic nRF5x Segger J-Link page to install and configure all the necessary software. Further information can be found in Flashing. Then build and flash applications as usual (see Building an Application and Run an Application for more details).

Here is an example for the Hello World application.

First, run your favorite terminal program to listen for output.

$ minicom -D <tty_device> -b 115200

Replace <tty_device> with the port where the board nRF21540 DK can be found. For example, under Linux, /dev/ttyACM0.

Then build and flash the application in the usual way.

# From the root of the zephyr repository
west build -b nrf21540dk_nrf52840 samples/hello_world
west flash

Debugging

Refer to the Nordic nRF5x Segger J-Link page to learn about debugging Nordic boards with a Segger IC.

Testing the LEDs and buttons in the nRF21540 DK

There are 2 samples that allow you to test that the buttons (switches) and LEDs on the board are working properly with Zephyr:

samples/basic/blinky
samples/basic/button

You can build and flash the examples to make sure Zephyr is running correctly on your board. The button and LED definitions can be found in boards/arm/nrf21540dk_nrf52840/nrf21540dk_nrf52840.dts.

Using UART1

The following approach can be used when an application needs to use more than one UART for connecting peripheral devices:

  1. Add devicetree overlay file to the main directory of your application:

    $ cat nrf21540dk_nrf52840.overlay
&uart1 {
  compatible = "nordic,nrf-uarte";
  current-speed = <115200>;
  status = "okay";
  tx-pin = <14>;
  rx-pin = <16>;
};

    In the overlay file above, pin P0.16 is used for RX and P0.14 is used for TX

  2. Use the UART1 as device_get_binding(DT_LABEL(DT_NODELABEL(uart1)))

See Set devicetree overlays for further details.

Selecting the pins

To select the pin numbers for tx-pin and rx-pin:

tx-pin = <pin_no>

Open the nRF52840 Product Specification 3, chapter 7 ‘Hardware and Layout’. In the table 7.1.1 ‘aQFN73 ball assignments’ select the pins marked ‘General purpose I/O’. Note that pins marked as ‘low frequency I/O only’ can only be used in under-10KHz applications. They are not suitable for 115200 speed of UART.

Translate the ‘Pin’ into number for devicetree by using the following formula:

pin_no = b\*32 + a

where a and b are from the Pin value in the table (Pb.a). For example, for P0.1, pin_no = 1 and for P1.0, pin_no = 32.